This invention relates to a medical device and more specifically to an ultrasonic tissue ablation instrument. Even more specifically, this invention relates to an ultrasonic medical treatment device with electrocautery. This invention also relates to an associated medical treatment method.
Many diseases of the brain and spine require surgery to provide the patient with relief. These could include cancer, non-malignant lesions and trauma induced by accidents or physical attack. As a procedure, neurosurgery has been practiced for several millennia. Archeologists have discovered evidence of sophisticated cranial surgery in relics and skulls dating back to Roman times. The tools found have been shown to be remarkably similar to today""s designs. Of course, modern science has substantially improved upon the techniques and results obtained in those days.
One of the biggest steps forward occurred approximately 30 years ago with the invention and marketing of the ultrasonic surgical aspirator. This device utilizes a hollow probe or tool that vibrates at frequencies at or above 20 kc with tip amplitudes of up to 300 microns. When the vibrating tip is placed against viable or diseased tissue, the moving tip ablates the cells and causes them to fragment or otherwise emulsify in the irrigation fluid that is being added simultaneously. The emulsified fluid is then aspirated through the hollow probe and deposited in a canister for histological examination or disposal.
The advantage of excising tissue with this device is that the surgeon can remove the lesion in layers almost 5 cells thick. By slowly removing the tumor from the top down, he can clearly see when he is reaching healthy tissue allowing him to stop before substantial collateral damage occurs. This is extremely desirable in brain and spine surgery, where tissue does not regenerate. Gastrointestinal surgeons have used the device as well for lesions of the liver and spleen, for the same reasons.
The required specifications, designs and engineering elements of such ultrasonic aspirators have become well known to the art in the intervening time. Although the technology is mature, several improvements can be made to enhance the ease of use and applicability to a wider range of procedures.
One side effect of any surgery is bleeding when the veins, arteries or capillaries are severed. Ultrasonic surgery is more sparing of blood vessels than knives because the collagen content of the vessels is more resistant to ultrasonic emulsion. However, the capillaries and small vessels will be compromised upon exposure to high amplitude ultrasonic tools. When these vessels are severed or punctured bleeding will of course occur. The surgeon will then be forced to pause the procedure, remove the ultrasonic tool from the site and generally reach for a cauterizing device of some type to close off the bleeder. Once coagulation has been achieved, then the surgeon can grab the ultrasonic tool, reposition it in the wound site and continue the removal of tissue. This situation repeats itself often in the course of the operation, lengthening the time of the procedure and coincidently the risk to the patient. It is therefore desired to find a way to cauterize tissue with the ultrasonic tool in place so the surgeon can stop bleeding with minimal downtime caused by switching tools and positions.
Several improvements to the basic design of the ultrasonic aspirator have been disclosed over the years which allows some degree of cauterization subsequent to or simultaneously with ultrasonic ablation. Most center on the application of RF cautery currents to the tool or probe itself. This has the effect of turning the ultrasonic tool into a monopolar RF cauterizer.
In a non-ultrasonic RF cauterizer, the tip of the tool is energized with a voltage sometimes exceeding 3000 volts RMS. The frequency of the voltage is very high, in order to prevent cardiac arrest in the patient. These frequencies are generally greater than 500,000 hertz. In monopolar RF, the tool is one pole of the electrical circuit. The second pole is generally a large piece of metal foil which the patient lays on during the procedure. The bare skin touching the foil makes an effective electrical contact. As the tool touches the tissue and the RF voltage is energized, a complete circuit path is created. The currents are very high, reaching 5 amps in some cases. At these currents, significant joule heating occurs in the tissue, raising the temperature higher than the burning temperature of 42xc2x0 C. Continued operation dries the tissue by evaporating the water content. Cauterization then occurs. Since the back plate is very large in relation to the tool tip, the current xe2x80x9cfans outxe2x80x9d as it leaves the tool tip and thereby lowers the current density in the tissue to a point where the temperature rise in the tissue is reduced to that below burning. This minimizes collateral burning and tissue damage.
However, as large as the plate is, some collateral damage occurs away from the bleeder site. This collateral damage cannot be controlled reliably by the physician and is of great concern when operating on the brain. If the damage is two widespread, mental capacity or memory may be affected negatively. In addition, electrical current is forced to flow through viable tissue to the ground plate. Again, neurological damage may occur in some organs that are susceptible to damage due to this current, such as the brain, heart and nerve bundles. Other organs, such as the liver or spleen, are less susceptible to current effects.
Researchers have found a way to minimize or eliminate this current path by designing a tool that includes two electrical poles or contacts. This is called bipolar RF cauterization. Here the current flows between the two poles through the intervening tissue. No current path to the back is allowed. Therefore, the tissue that is damaged is only that caught between the two contacts, which can be very small.
Designers have found a way to add monopolar cautery to ultrasonic devices by connecting one electrical contact to the vibrating tip of the ultrasonic device. Several patents have disclosed concepts and techniques for this, such as U.S. Pat. No. 4,931,047 to Broadwin, et al. Here, the tip of the ultrasonic tool is the single pole that touches the tissue. The surgeon will generally stop ultrasonic vibration and turn on the cautery voltage. Current leaves the tip of the probe and goes through the body to the back plate. This has been shown to be effective in eliminating the need for switching tools to stop bleeding, saving time and effort on the doctor""s part. However, all of the detriments of monopolar cautery still exist. Neurosurgeons are especially reticent to allow significant current to flow through brain or spinal cord tissue for fear of inducing neurological damage. In addition, the piezoelectric crystals of the ultrasonic transducer stack must be isolated from the cautery voltage or damage to the transducer or electronics will occur.
It is an object of the present invention to provide an ultrasonic treatment device or instrument having electrocautery capability.
Another object of the present invention is to provide such a device that eliminates the above-described deficiencies in conventional systems.
A further object of the present invention to provide such a device or instrument which is easy to use and which provides reliable cautery effects while minimizing patient risk during an ultrasonic aspiration procedure.
Yet another object of the present invention is to provide such a device or instruments with a capability of grasping and clamping tissue or vessels prior to and concurrent with electrocautery.
A related object of the present invention is to provide an associated method which combines ultrasonic ablation with electrocautery in a manner that is easy to use.
An ultrasonic medical treatment device pursuant to the present invention comprises a casing, an elongate probe, a transducer assembly, a sheath and a plurality of electrode members. The casing is generally in the form of a handpiece which facilitates manipulation by a surgeon. The probe is mounted to and extends from the casing and has an axis and a free end serving as an operative tip. The transducer assembly is mounted to the casing and is operatively connected to the probe for generating vibrations of at least one ultrasonic frequency in the probe. As is well known, the ultrasonic vibration frequency is a resonant frequency of the probe, whereby standing waves are produced in the probe. The sheath surrounds the probe. The electrode members are connectable to an RF voltage source and are mounted at least indirectly to the casing so as to permit relative motion between the electrode members and the probe.
In a preferred embodiment of the invention, the electrode members are attached to the sheath, which is movably mounted to the casing. It is also preferred that the electrode members are fixed to and substantially embedded in the sheath. The electrode members have exposed portions disposed proximately to the operative tip of the probe for forming electrically conductive contact with organic tissues at a surgical site in a patient.
More particularly, the sheath is movably mounted to the casing for reciprocatable motion along the axis of the probe, whereby the tip of the probe may be alternately covered and exposed. Thus, during an ultrasonic use of the instrument, the sheath is retracted to expose the operative tip of the probe, which is energized by a predetermined ultrasonic vibration produced by the transducer assembly. Should a blood vessel become severed by ultrasonic ablation, the action of the transducer assembly is interrupted and the sheath slid forward, in a distal direction, to cover the tip of the probe and to facilitate contact between the exposed portions of the electrode members and the region about the severed blood vessel. The electrode members are then connected to a radio-frequency current source to generate a current flow between the exposed portions of the electrode members.
The electrode members may be exactly two in number. In that case, the exposed portions of the electrode members are preferably disposed at an angle of less than 90xc2x0 from one another. However, in some applications it may be preferred to have the exposed portions of the electrode members angularly spaced by a greater angle, up to 180xc2x0.
In another embodiment of the invention, there are two or more pairs of electrode members, with the members of each pair being disposed adjacent to one another along the circumference of the sheath. In this embodiment, a manually operable switching circuit may be operatively connected between the power source and the electrode members for determining which pair of electrode members is to be energized. The operating surgeon selects that pair of electrode members which is most closely located to a bleeding site.
Pursuant to another feature of the present invention, the electrode members are movable in parallel to the axis of the probe.
A medical surgical method in accordance with the present invention utilizes an ultrasonic medical treatment device having a casing and an elongate probe mounted to and extending from the casing, the probe having an axis and a free end serving as an operative tip, a transducer assembly mounted to the casing being operatively connected to the probe, a plurality of electrode members being mounted at least indirectly to the casing. The method comprises inserting a distal end portion of the probe into a patient, thereafter energizing the transducer assembly to generate a standing wave of an ultrasonic frequency in the probe, ablating tissues of the patient at the operative tip of the probe during the generating of said standing wave, connecting the electrode members to an RF voltage source, and cauterizing tissues in the patient owing to the conduction of current between exposed portions of the electrode members.
Pursuant to another feature of the present invention, the electrode members are moved relative to the probe, thereby placing the exposed portions of the electrode members in a predeterminable location relative to the operative tip. Where the electrode members are connected to a sheath, the moving of the electrode members may be accomplished by shifting the sheath relative to the probe.
In a further embodiment, the two electrodes may be spaced 180 degrees apart and be hinged nearer the proximal end of the sheath. Two protuberances may be provided, extending outside the outer sheath assembly, which contact the rigid metal electrodes. By sliding the sheath forward, the distal ends of the electrodes are exposed. These electrodes may be manipulated by the surgeon to allow tissue to fill the gap between said electrodes. By squeezing the protuberances, the surgeon may apply a pinching force on the tissue to help close severed vessels while applying electrocautery current.
It is to be noted that the electrodes may be used to ablate tissues of the patient in addition to cauterizing the ablated tissues.